Electrostatic condenser



June 29, 1943. w. DORN ELECTROSTATIC CONDENSER Filed Feb. 16, 1940 2 Sheets-Sheet 1 June 29, 1943. w. DORN ELECTROSTATIC CONDENSER Filed Feb. 16, 1940 2 Sheets-Sheet 2 Jnrenfaf:

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i above outlined. but without success.

Patented June 29, 1943 ELECTROSTATIC CONDENSER Walter Dorn, Vaihingen-Rohr, Germany; vested in the Alien Property Custodian Application February 16, 1940, Serial No. 319,340

In Germany March 15, 1934 8 Claims.

This invention relates to electrostatic con- ,densers and particularly to those called wound strip condensers.

The ultimate object of the invention is to provide at a reasonable .price a condenser having good efliciency, a capacity high in relation to the volume and also in relation to the weight of the 'condenser while at the same time. being very durable in use, that. is, having a relatively high resistance to puncture and excellent self-healing properties. Condensers constructed according to this invention may be-made for any desired use including relatively high tension work.

Many attempts have been made heretofore to provide a condenser meeting the requirements Such attempts have involved the use of wound paper strips serving as a dielectric. With such paper strips the electrodes or conductors were either of metal foil or of metal in finely divided, dis-' crete particles placed upon paper strips and then calendered.

Condensers of the formerv type, viz: those having metal foil conductors, have been known and used since the early history of the condenser art and are entirely satisfactory for many purposes. Since, however, the manufacture of a thin foil involves expensive hand labor, and very thin foil cannot be made reliably from ordinary commercial metals, but only from noble metals, particularly gold, and because these are prohibitively expensive, it has not beenfpossible with foil conductors t produce a condenser for commercial use which will satisfy the demands of ,the art for a condenser having a high capacity relative to its volume and weight under usual operating conditions at a reasonable cost.

Condensers of the latter type, namely, come prising paper strips with metallic coatings of discrete particles placed thereon, were on the market for some years, but owing to serious defects inherent in such construction were unsatisfactory and have been abandoned. The basic defects of such a condenser arise forthe reasons, first, that the discrete particles of metal on the paper are not all of the same size; second, that such particles deposit themselves erratically, so that some parts of the paper are not coated, and third, the particles do not themselves coalesce on the paper. The metal coating when deposited is not a good conductor, even on the coated portions of the paper, and hence the coated paper strip had to be subjected to a calendering process, on the hypothesis that in this way the squeezed into close metallic contact with each other to form a conductive coating. Since, however, the metal coating as deposited was not and could not be of uniform thickness, the calendering process produced a level outer metal surface but at the expense of the dielectric value of, the paper carrier. The thicker portions of the coating, and particularly the particles of metal of larger size, were forced more deeply into the paper than the thinner parts of the coating or the smaller particles. As a result of this, the

- intensity of the electric field and dielectric value of the paper were notuniform over the whole area of thestrip, but contained not only spots operating conditions at voltages which the con- I ensure that a puncture would occur.

denser was supposed to endure with safety. In other words, the condenser not only had a low resistance to puncture at certain points but developed an increased intensity of field at such weakest points. But, what was equally as serious, it had poor self-healing properties. is meant by this -is that when punctured, which of course causes ashort circuit, the latter did not quickly destroy itself and restore the condenser to operative condition while still retaining a sutliciently high percentage of its original capacity value t permit it to continue to function. in the circuit. Experience shows that sometimes appreciable areas of the conductor had a considerable number of the larger particles so that glowdischarges occurred at such areas during normal operation, whereby carbonization of the dielectric paper took place, so that in time a short circuit of the condenser might occur over a relatively extensive area, thereby rendering the condenser useless, even if no puncture occurred. Of course, such glow discharges and the resultant carbonization of the paper tended to increase the chances of puncture, in fact to One hypothesis as to the action which takes place in self-healing is that when the dielectric is punctured, which forms a hole in the paper, the short circuit is supposed to continue sufllciently to melt the metal around the edge of the hole and then the surface tension of the molten metal'and the cohesive force between the said molten metal and the adjacent solid metal of the coating would cause the molten metal to be attracted back away from the hole, thereby inmetal particles would be flattened and thereby creasing the length of the air path for the elec- What tric current from the edges of the metal of one conductor to the edges of the other conductor. Also, in connection with this hypothesis it was considered highly disadvantageous to have any vaporization of the metal of the conductor during the short circuit, since such metallic vapor was assumed to bring about injury to the condenser.

For this reason it was the general practice to employ a metal for the conductor of such a character that while relatively low melting it had a relatively high vaporizing point, as, for example, tin.

Since the actual results attained by the condensers of the prior art were unsatisfactory, applicant proceeded to use a metal for condenser conductors which while relatively low melting had also a relatively low temperature of vaporization. Where the prior art was wedded to the use of tin, applicant employed zinc or cadmium and because of the fact that said metals vaporized at a low temperature, applicant was enabled to apply the metal coating to the paper by a process of thermal vaporizing without injury to the paper. whereby it became possible to obtain a well-adhering coating of substantially uniform thickness, homogeneous and electrically conductive throughout its full extent and of relatively lower resistivity; all these results being obtained in the coating as originally deposited on the paper, thereby making calendering unnecessary and so maintaining substantially the full dielectric value of the carrier paper. The metallic coating had the characteristics of a sheet of metal of uniform thickness cut from a solid body of the same metal. Since such a solid body of the same metal is always formed primarily by casting, such metal has the properties 01 metal set from a liquid state. It is to be observed that applicants coating is much thinner than any sheet cut from a solid body. However, as the result of a long series of experiments, it was found that the desired results could not be obtained unless the thickness of the metallic coating was kept within a range of about 200 to 25 millionths of a millimeter. Below this range the coating was likely to be imperfect and not sufficiently conductive. At thicknesses materially above this range, although the reslstance to puncture might be satisfactory, the self-healing properties were not. That is to say, puncture tests showed that with coatings thicker than 200 millionths mm. there was a failure of an appreciable percentage of the condensers to restore themselves to a capacity sufflciently approaching the original capacity of the condenser to permit continued use and the percentage of loss increased with the increase in thickness. The standard for the minimum value of a suitable condenser is 200 megohm microfarad used by the German postal authorities and generally accepted by the art.

For the purpose 01' attaining the ultimate object of the invention hereinbefore recited and to avoid all the disadvantages which existed in wound condensers of the prior art, a condenser embodying the present invention comprises a plurality of wound strips of thin sheet dielectric material, more particularly paper, serving as a conductor support, each of which is provided with an adherent, uncalendered coating of relatively low melting metal having a relatively low temperature of vaporization and relatively low resistivity, such as zinc or cadmium, said coating being homogeneous and of substantially uniform thickness not materially exceeding 200 millionths of a mm., and not less than 25 millionths of a min., such coating having substantially all the specific electrical and physical characteristics of a layer cut from a solid body of the same kind of metal. In the best embodiment of the invention the condenser also has metallic terminal connections united to and integral with the edges of said metal coatings, these terminal connecting portions having the properties of metal, such, for example, as tin, sprayed onto the edges of the metal coatings, and connected to a suilicient length of such edges to form a good conductive connection, thereby not only preventing undue heating by the electric current along the line of union and within the adjacent part of the coating, but avoiding all difliculties arising from the use of the very thin coatings which are employed in applicants condensers. Furthermore, in the best embodiment of the invention, each terminal, although connecting with a considerable length of the edges of the respective coating at the respective faces of the condenser, does not cover each face completely but is arranged so as to leave openings to permit ready access of impregnating material to the interior of the condenser.

By this arrangement of the terminal connections it becomes possible to apply the terminals to the condenser before impregnating it, whereas in the prior art the reverse practice was followed, with the consequence that it was difficult after the impregnation of the condenser to make a good union between the edges of the coating and the terminal metal.

The invention will now be described more specifically in connection with the accompanying drawings, in which- Fig. 1 is a diagrammatic perspective view partly in section illustrating one form of condenser embodying the present invention, the interior elements being shown on greatly enlarged scale.

Fig. 2 is a diagrammatic view in elevation illustrating one type of apparatus suitable for producing a metal coating of the kind employed in the condenser of the present application, on a strip of dielectric material such as'paper.

Referring to Fig. l, (1 denotes a paper strip carrying an adhering metallic coating c, while I) indicates the companion paper strip carrying an adhering metallic coating d.

From the sectioned portion of Fig. 1 it will be seen that the metallic coating 0 extends to the margin of its carrier-paper strip a at the side shown upmost in the drawing while at the oppo' site side the metal coating 0 stops considerably short of the corresponding margin of said paper strip a. The coating d carried by the paper strip b is oppositely arranged with relation to its strip, that is, it extends to that margin of its paper strip b which is shown in the drawing at the lowermost side of the condenser but does not extend to the other margin of said strip. The metallic coatings c and d serve as the conductors of the condenser, it being understood that when included in the circuit the conductors are of opposite polarity, one being positive and the other negative, depending on the manner in which the condenser is connected to the circuit.

It will be seen that the paper strips a and b serve not onl as carriers of the metal coatings but also as dielectrics between the coatings. In some cases, and particularly in th present example, there is provlded additional dielectric material consisting of two plain paper strips as indicated at J and g, both being narrower than the metallically coated paper strips a and b. Strips I and a are displaced laterally with relation to each other, one margin of strip ,g being in register with one margin of each of the coated strips a and I), while the corresponding opposite margin of strip 1 is in alignment with the correspondingopposite margins of strips 17 and a, as will be clear from Fig. 1. By this arrangement a pocket, groove, or interspace is formed for the reception of metal sprayed onto the faces of the condenser and a small portion of one surface of each metallic conductor is exposed in the respective interspace so as to receive the sprayedon metal. By filling up, at least partly, the interspace at the two faces or front sides of the condenser with sprayed-on metal which also extends as a layer across the respective face of the condenser, forming a good conducting body w, all the turns of the'same metal coating ar connected together, in parallel, to the corresponding terminal connection so that a large surface is available for the entrance of current into the coating, thereby avoiding losses due to heating, as would occur with terminal connections of restricted area and conductivity, which would cause high current density at the contact between the terminal connections and the respective condenser conductors.

For the purpose of providing a strip of dielectric material with a firmly adherentcoating of substantially uniform thickness of homogeneous low-melting metal having a low vaporizing temperature, where such thicknesshas a size in the range of about 200 to 25 millionths 'mm., a very satisfactory process is to vaporize the metal in a vacuum, deposit it on the dielectric while still in a vacuum and so conduct the process as to temperature conditions that the metal will pass from the vapor state to the solid state so rapidly that there is not sufficient time for the formation of liquid globules, as would occur if the vapor was allowed to cool slowly and gradually pass through the liquid state.

The particular process which applicant considers best for attaining the desired result will now be described in connection with apparatus illustrated diagrammatically in Fig. 2.

The apparatus comprises a vacuum chamber, which as illustrated is in the form of a hollow cylinder, having one end permanently closed by an end wall and the other end arranged to be closed air-tight by a door or lid. The peripheral wall is indicated at :r, Fig. 2, the permanent end wall at y, and the door or lid at k. As illustrated, the door is hinged to the wall at. Any suitable means for locking the door to the wall and for maintaining a perfect air-tight seal may be employed, such as a copper or other gasket inserted in a grooved flange f the door, and bolts and nuts, machine screws or clamps for drawing the door tightly against the end of the hollow cylinder. As the particular details of such means for securing the lid to the open end of the cylinder to make and maintain a perfectly tight Joint, form no part'of the present invention and are readily supplied by those skilled in the art, they are not shown.

For the purpose of producing and maintaining a high vacuum in the vacuum chamber, a suitable conduit h is provided of relatively large cross-sectional area which connects to the inlet of a good vacuum pump (not shown) capable of producing quickly and continuously maintaining in the vacuum chamber an absolute pressure as low as one one-hundredth of a-millimeter (0.01

mm.) mercury, which high vacuum necessitates that the vacuum chamber should be absolutely air-tight or at least as near to that ideal as possible toobtain in practice. With such a vacuum and no leakage, the process carried out within the vacuum chamber, a hereinafter described, will be under substantially non-oxidizing conditions.

Within the vacuum chamber there is provided a crucible for receiving the metal to serve as a coating, means for heatin the crucible in order to vaporize the metal, a cooling jacket surrounding the crucible and its heating means to prevent the passage of heat from the heating means to its exterior, and means for feeding a paper strip continuously at any required velocity, across and close to the mouth of the crucible, which is in the form of a narrow slit whose length is transverse to the direction of travel of the paper strip, the length of the slit being such as to cause a deposit of solid metal on the paper strip of the required size measured transversely of the strip. The distance of the surface of the paper strip from the mouth of the crucibl is such, and the temperature of the paper is so maintained that the metallic vapor has not time to cool and coalesce into liquid drops before reaching the surface of the paper but still maintains its vaporous condition and when striking the colder paper is immediately cooled to solid form.

In the particular apparatus shown in Fig. 2, the permanent end wall of the vacuum chamber is provided with a fixed spindle l to receive a bobbin on which is rolled the paper strip to be coated, this bobbin having a flange l of 800d conductive metal such as copper, in which eddy currents may be excited, the flange being arranged in close proximity to a brake device which as shown comprises an electromagnet 0 whose field will produce eddy'currents in the flange I, and thereby develop a braking action to check the rotation of the flange F and hence to control the unrolling of the paper strip. The field strength of the electromagnet v may be adjusted by varying the current through its coils, in any usual way. For this purpose the. circuit connections of the electromagnet may be extended outside the vacuum chamber, suitably sealed leading-in wires serving to make an air-tight seal where the wires pass through the wall of the vacuum chamber.

There is also provided a rotatable winding bobbin m, mounted upon a spindle 1n. and arranged to wind up the strip of metallized paper. Any suitable means for rotating the bobbin m may be employed. Such means may be located in the vacuum chamber or the spindle ml may be a live spindle, extending outward through the. permanent wall of the vacuum chamber and rotated by any desired power means, in which case a suitable air-tight seal must be employed around the live spindle.

The strip is passed over suitable guide rollers as indicated at t, t, t', t, to lead the strip from the bobbinl to the bobbin m, and to provide a substantially horizontal runof the strip in close vicinity to the mouth of the vaporizing device. This vaporizing device consists of a suitable crucible n having a cap n which may be detachable. The crucible and its cap should be made of suitable metal such as iron, and they are most advantageously connected by a telescopic joint, the crucible fittinginto its cap, as shown in Fig. 2. The cap 11 of the crucible has a mouth formed as small slit p, which extends transversely to the direction of travel of the paper,the length of the slit being such as to give the desired width of metal coating on the paper. By making the caps detachable from the crucible, an assortment of caps with slits of different lengths of slits may be provided, so that different widths of coatings may be applied to the paper strips.

The crucible and its cap are supported inside a heating device consisting of a vessel provided with heating coils one, 1'', of whose terminals is led through the permanent wall of the container, from which it is suitably insulated. The other terminal of the heating coil may be grounded on the inside of the wall of the vacuum chamber, and the electric connection of the source of electricity may be made on the outside of such wall for one polarity' and to the terminal, 1', which extends outside the vacuum chamber, for the other polarity.

While the crucible and its cap may be supported in various ways, in the best embodiment of the invention the joint between the crucible and its cap, may be screw-threaded, or provided with a bayonet connection, or with a set-screw in order to lock the two together, in which case the cap may be provided with a flange fixed to it and arranged to rest on the top of the heating device, whereby the crucible and cap are suspended so that the bottom of the crucible clears the bottom of the heating device.

To prevent the heat of the heating device escaping into the remainder of the space within the vacuum chamber, there is provided a suitable cooling jacket surrounding the heating coils as indidlted at a, this being connected by inflow and oiitilow tubes s and s leading to a circulating pump, not shown, whereby any suitable cooling liquid, for example, water, may be circulated through the jacket.

It will be noted that the cooling jacket extends beneath the heating device, and as it cannot extend above the latter, there is provided some heat insulating material at the upper end of the heating coils to reduce the amount of heat escaping at the top.

In using the device, the door of the vacuum chamber is opened, a bobbin carrying a rolled-up strip of paper is placed upon the spindle 1 the end of the strip drawn off, passed around the respective guide-rolls, and secured to the winding-up bobbin.

The crucible and its cap are lifted up to free them from the heating device, and removed. The cap is unlocked and removed from the crucible body. A charge of low-melting metal, such as zinc or cadmium, is inserted in the crucible, the cap is secured in place thereon and the two returned to the space within the heating device.

The door of the vacuum chamber is closed and secured air-tight. The circulating means for the cooling water may be started in action to circulate water through the jacket. The vacuum pump is set in action and the pressure in the vacuum chamber is reduced to about 0.01 mm:

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Current may then be turned on to the heating coils and after such a time as is required to cause melting of the metal in the crucible and the evolution of vapors therefrom, the motor driving the live spindle m is started, whereupon the paper strip begins its travel and the vapor of metal deposits continuously on the lower face of the paper strip as a solid metal coating of a thickness less than 200 millonths mm., but not less than 25 millionths mm.

The thickness of the coating is determined by the rate of travel of the paper strip. If the strip is fed very rapidly, a coating even less than 25 millionths mm. may be produced, but in practice there may be some diillculty in producing a reliable coating.

The strip may be run slowly enough to give a coating of metal as thick as 200 millionths mm., without danger of injuring the paper by heat.

Although the temperature of the crucible is of course sufficient to vaporize the metal within it, the cooling jacket and heat insulation at the top of the heating coil are sufficient to prevent radiation of heat into the rest of the space in the vacuum chamber and on account of the high vacuum employed there can be substantially no transfer of heat to the paper strip except that carried by the metallic vapor itself. Hence, the paper strip as it comes up to the mouth or slit of the crucible cap is relatively cold, that is to say, it is about ordinary room temperature and need not be in excess of 30 C., so that the vapor, which strikes the paper almost as soon as it leaves the crucible mouth is immediately chilled to the solid state so that there is no time for surface tension to act and cause spheroidal formation of the metal in the liquid state. The strip may be located 0.5 to 2 mm. from the slit.

By the use of the high vacuum, which should be maintained between 0.01 and 0.05 mm., mercury, the temperature of vaporization of the metal is lowered to an appreciable extent, danger of oxidation of the metallic vapor is avoided and, of course, there is no possibility of occlusion of gas to form bubbles in the coating metal.

At the completion of the process of coating the paper, the heating current is cut off and the motor which drives the live spindle m is stopped. The circulating pump for the cooling water may be retained in operation because of the reserve heat stored'in the crucible and in the metal parts of the heating device.

The vacuum pump may be cut off and the vacuum broken, so that the door may be opened and the bobbins with the paper withdrawn.

Another pair of bobbins and paper may be put in place on the spindles and the operations conducted as before described.

It will be found that the temperature of the vapor from the metal will itself have some effect on the thickness of the metallic coating deposited on the paper strip, and such temperature may be regulated by controlling the heating current, although the main controlling factor is the velocity of the paper across the mouth of the crucible cap.

While applicant has given the range of 200 to 25 millionths mm. as that within which successful results may be obtained, it has been found that there is a great advantage in having the thickness maintained such that it will be in the range to 25 millionths mm. and in regular practice for ease in carrying out the process the latter range is generally employed. It is possible to produce a coating of definite substantially uniform thickness throughout the length of a strip, so that in stating that the thickness falls within the range 200 to 25 millionths mm. it is to be understood that this does not mean that the metal coating on a given strip varies between these thicknesses. It merely means that a condenser having a uniform coating of substantially uniform thickness throughout its length and breadth will be satisfactory if the dimension is not greater than 200 millionths mm. and not less than 25 millionths mm. and most advantageouslynot greater than 100 millionths mm.

After the desired metallized paper strips have been made they are used in the manufacture of a condenser. Two such metallized strips with intervening narrower plain paper strips alternating with the metallized paper strips, as shown stated hereinbefore, the thinness of the coating makes necessary a special construction of such terminal connection and in carrying out the present invention this is obtained by spraying on metal by the Schoop spraying process, which interferred, and could not be entirely removed withoutmuch difllculty and expense, 3

Since, however, in the best embodiment of the invention applicant makes a conductive connection not only with the extreme edges of the conductors, but also with a small portion of the pregnating material may reach the interior of comprises forcing a stream of finely divided or molten metal through a blow-pipe home under gas pressure, the stream as it issues from the apparatus being played with movement upon the respective faces of the condenser. The metal employed is one which while relatively lowmelting is not one which volatiliz es at as low a temperature as the metallic coating metal on the paper.

Tin is well adapted for this purpose because it can-be sprayed in the open atmosphere without objectionable oxidation, and because the layer forming a terminal connection may be built up readily to a sufficient thickness to provide good conductivity, the final construction is such as to avoid any injurious heating.

- The sprayed-on metalforms a good integral union with the edgesof the metal whichcoats the aper and by moving the stream of sprayedon metal undue heating of the condenser is avoided. It will be'noted from the description hereinbefore given that in the best embodiment of the invention not only is the union made with the extreme edge of each condenser conductor, but with a small margin of the exposed face of the respective conductor thereby greatly increasing the area of contact of the conductor and terminal connector. The Schoop process lends itself well to this method of making terminal connections with the margins of the faces of the condenser conductors because the temperature and the velocity of the sprayed-on metal may be made such asto drive the metal down into the interspaces provided in the faces of the condenser without injury to the paper by overheating and yet without undue cooling of the metal which is being sprayed.

In the prior art when terminal connections were made by the application of'molten metal to the edges of condenser conductors, the entire face'of the condenser was coated.- As it is necessary to impregnate'a condenser with an'insulating material, usually parafiine wax, the prior pra'ctice-ofcoating the entire face of the condenser with a terminal connecting layer-made it necessary to carry out the impregnating process before the terminal metal was applied to -the edges of the condenser. Hence, it was difficult,

if not practically impossible, to make a good metallic connection between the edge of the condenser conductor and the metal of the terminal because the wax of the impregnating material the condenser in a way to permit full saturation of the paper and the escape of any air. As a consequence of this feature of applicant's invention it becomes possible to apply first the terminal connection layer of metal, whereby a good integral union is readily obtainable, and thereafter subject the condenser to the impregnating process.

In impregnating the present condensers it has been found advantageous to employ a well known synthetic parafllne, which is completely non-hygroscopic. Material of this kind is heated appreciably above its melting point. For example, with such a synthetic parafllne having a J melting point of 103 C., it will be found well to apply it and maintainit and the condenser at 130 C. In carrying out this step the condensers are placed in avacuum'chamber and the air as completely exhausted as possible, for example, down to an absolute pressure'of 0.01 mm.

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Thereafter, the vacuum chamber is charged with the hot impregnating solution, covering the condensers but not entirely filling the vacuum chamber.

The condensers of the present invention on account of the uniform thickness of the metal coating and of the intervening dielectric, do not in use have points of increased intensity of electric field, but have a substantially uniform field at all points of the dielectric. Consequently the condensers are well able to sustain the working voltages for which they are designed, and if due to an accidental temporary increase in voltage apuncture should occur, this is healed immediately without appreciable loss of capacity. In practice the condensers of the invention have been subjected to repeated punctures and have still retained an R. C. value above the minimum value laid down by the German postal authorities. 7

The efficiency is high because of low losses from heating and inductive edge effects. What is also of the greatest importance is the small volume and weight for a given capacity, which makes the condenser extremely valuable in radio work, particularly in aeroplanes.

The invention set forth and claimed in the present application was embraced in the disclosure and included in the claims of application Serial No. 9,877; filed by this applicant March 7, 1935, so that the present application is filed as a continuation of said'prior'applicatlon.

The terms low-melting point and low-vaporizing point are used in the specification and claims to define metal whose melting point and vaporizing point are of the same general order as those ofzinc or cadmium.

' What I claim is:

ing an adherent metallic coating of metal selected from the group zinc. cadmium, said coating having the homogeneity and other specific characteristics of the same metal cut from a solid body, said coating being of substantially uniform thickness whose dimension is not greater than 200 millionths mm. and not less than 25 millionths mm., said condenser having for each coated strip a common terminal connector united to a plurality of turns of its respective coating,

2. An electrostatic wound condenser comprising at least two metallized dielectric strips wound in a plurality of turns. each strip carrying an adheret metallic coating of metal selected from the group. zinc. cadmium, said coating having the-homogeneity and other specific characteristics of the same metal cut from a solid body. said coating being of substantially uniformthickness whose dimension is not greater than 200 millionths mm. and not less than 25 millionths mm., said condenser having for each of said two coated strips a common terminal connector united integrally with a plurality of turns of its respective coating.

3. An electrostatic wound condenser comprising at least two metallized dielectric strips wound in a plurality of turns, each strip carrying an adherent metallic coating of metal selected from the group. zinc. cadmium, said coating having the homogeneity and other specific characteristics of the same metal cut from a solid body. said coatingbeing oi substantially uniform thickness whose dimension is not greater than 100 millionths mm. and not less than 25 millionths mm., said condenser having for each coated strip a common terminal connector united to a plurality of turns of its respective coating.

4. An electrostatic wound condenser comprising at least two metallized dielectric strips wound in a plurality of turns, each metallized strip carrying an adherent metallic coating of metal selected from the group, zinc, cadmium, said coating having the homogeneity and other specific characteristics oi the same metal cut from a solid body and being of substantially uniform thickness whose dimension lies within the range 200 to 25 millionths mm., the width 01 each coating being less than the width of its dielectric strip and extending to one margin only of its strip, the strips being arranged in the condenser so that the metal coating at the margin of one strip will be at one face of the condenser and the metal coating at the margin of the other strip will be at the other iace of the condenser, all the turns of each coating being connected by an integral union to its respective terminal connection comprising a solid body of metal having the characteristics of sprayed-on metal.

5. An electrostatic wound condenser comprising at least two metaiiized dielectric strips and alternating plain dielectric strips, all the strips being wound together in a plurality of turns. each metallmed strip carrying an adhereat metallic coating of metal selected from the group, zinc. cadmium. said coating having the homogeneity and other specific characteristics of the some metal cut from a solid body and being of substantially uniform thickness whose dimension lies within the range 200 to 25 millionths mm., the width of each coating eing less than the width of its dielectric strip and extending to one margin only of its strip. the strips being arranged in the condenser so that the metal coating at the margin 01 one strip will be at one face of the condenser and the metal coating at the margin of the other strip will be at the other face of the condenser, the plain dielectric strips having widths less than the width of the metallized strips, one margin of each plain strip registering with the uncoated margin of its adjacent metallized strip, whereby interspaces are formed exposing a margin oi the metal coating of the adjacent strip. allthe turns of each coating being connected by an integral union to its respective terminal connection comprising a solid body of metal having the characteristics of sprayed-on metal extending into the respective interspaces and united to the said exposed marginal portions of the respective coating.

6. An electrostatic wound condenser comprising at least two metallized dielectric strips wound in a plurality of turns, each strip carrying an adherent metallic coating of metal having a relatively low melting point and also a relatively low vaporizing point, said coating having the homogeneity and other specific characteristics of the same metal deposited and cooled quickly from vapor of such metal, said coating being of substantially uniform thickness whoae dimension is not greater than 200 millionths mm. and not less than 25 millionths mm., said condenser having for each coated strip a common terminal connector united to a plurality of turns of its respective coating.

7. An electrostatic wound condenser compnsing at least two metallized dielectric strip wound in a plurality of turns, each strip carrying an adherent metallic coating of metal having a relatively low melting point and also a relatively low vaporizing point, said coating having the homogeneity and other specific characteristics of the same metal deposited and cooled quickly from vapor of such metal. said coating being of substantially uniform thickness whose dimension is not greater than 200 millionths mm. and not less than 25 millionths mm., said condenser having for each coated strip a common terminal connector of solid metal having the properties of metal sprayed upon the edges of the coatings by the Schoop process and united to a plurality of turns of its respective coating.

8. An electrostatic wound condenser comprising at least two metallized dielectric strips wound in a plurality of turns, each strip carrying an adherent metallic coating of metal having a relatively low melting point and also a relatively low vaporizing point. said coating having the homogeneity and other specific characteristics of the same metal cut from asolid body. said coating being of substantially uniform thickness whose dimension is not greater than 200 millionths mm. and not less than 25 millionths mm., said condenser having for each coated strip a common terminal connector united to a plurality of turns of its respective coating, each terminal connector covering only a part of each front side oi the condenser so as to leave a space for the admission of the impregnating material.

WALTER DORN. 

